Patent Documents 1 and 2 to be indicated below each disclose an easily openable container lid for a container accommodating a gas-containing liquid, in particular, accordingly a container whose interior is brought to a positive pressure after its mouth-neck section is mounted with a container lid for sealing, the easily openable container lid being composed of a shell which includes a circular top panel wall, a skirt wall extending from the peripheral edge of the top panel wall arcuately in a radially outward and downward direction and then extending downwardly vertically, in a vertical sectional view, and a gripping piece extending out from the lower end of the skirt wall, and a disk-shaped synthetic resin liner disposed on the inner surface of the top panel wall of the shell. The top panel wall, the skirt wall, and at least the base of the gripping piece, of the shell are formed from a metallic sheet such as an aluminum-based alloy sheet. The shell is further formed with a pair of scores having first portions extending upwardly on the skirt wall from both sides of the gripping piece, and second portions continuous with the first portions and extending at the peripheral edge of the top panel wall. The liner is formed by embossing a synthetic resin material on the inner surface of the top panel wall of the shell. The second portions of the pair of scores are located radially inwardly of the outer peripheral edge of the liner. In order to avoid the inhibition of breakage because of the presence of the liner in breaking the second portions of the pair of scores, the liner is brought into a state of non-adhesion or weak adhesion to the inner surface of the top panel wall of the shell at least in a region where the second portions of the sores extend.
Patent Document 3 indicated below discloses an easily openable container lid for a container accommodating a liquid in a heated state, accordingly, a container whose interior is brought to a negative pressure after its mouth-neck section is mounted with and closely contacted with a container lid, the easily openable container lid which has an annular groove formed in a thick-walled peripheral end section of a liner, and in which opposite-side parts demarcated with such a groove are rendered deformable without interfering with each other, so that even when an impact is applied to the container lid mounted on the mouth-neck section of the container, damage to the sealing of the mouth-neck section is avoided if possible.